The decline in breast cancer incidence is partly due to a reduction in what?

The decline in breast cancer incidence is largely attributed to a reduction in postmenopausal hormone replacement therapy (HRT). Over the years, studies have shown that the use of HRT, particularly combined estrogen and progestin therapy, is associated with an increased risk of developing breast cancer. In 2002, results from the Women's Health Initiative study revealed this alarming connection, leading to a significant decrease in the use of HRT among postmenopausal women.

This decline in HRT usage has been correlated with a subsequent decrease in breast cancer rates, as fewer women exposed to hormones that can stimulate the growth of hormone-receptor-positive breast cancers may ultimately lead to lower incidence rates in the population. The other options, such as chemotherapy, radiation therapy, and preventive mastectomies, are treatments or preventive measures that do not have a direct causal relationship with the overall incidence of breast cancer; rather, they are typically applied after a diagnosis has been made or used as interventions to reduce risk in specific, high-risk populations.